The plant phenylpropanoid pathway supplies molecules used in pigmentation, response to pathogen attack, and induction of Rhizobium nodulation genes. As medicinal natural products, the phenylpropanoids are potential cancer chemopreventive, estrogenic, and anti-oxidant compounds. Chalcone synthase (CHS) is the key regulatory enzyme in the pathway and conducts a complex series of decarboxylation, Claisen condensation, cyclization, and aromatization reactions at a single active site. Metabolically, chalcone isomerase (CHI) catalyzes the highly stereospecific and very rapid reaction immediately following formation of chalcone by CHS. Given the quality of the CHS crystals (1.55 E diffraction at the Salk), use of very intense X-rays from a synchrotron source and cryo-cooling could yield diffraction at atomic resolution and provide detailed information about the reaction mechanism. Diffraction quality crystals have been obtained for CHI (3 E), however, the unit cell is quite large (a = 89.43 E, c = 353.08 E), making CHI an excellent candidate for data collection using an intense X-ray source.